The Little Ice Age, which spanned from the early 14th to the mid-19th century, was a period of significant cooling, with global temperatures dropping by up to 2°C, particularly in the northern hemisphere. During this time, glaciers expanded, and harsh climate conditions marked the landscape, leaving an imprint that persists into the present day. One area significantly impacted by these changing climatic conditions is the Mont-Blanc massif in the French Alps.
A new study published in Earth and Planetary Science Letters has delved into the region’s response to climate change, specifically looking at how the massif has evolved since the end of the Little Ice Age around the 1850s. Led by Dr. Léa Courtial-Manent from the Université Savoie Mont Blanc, the research focuses on understanding how the mountain range’s landscape has eroded over the past several centuries, particularly by studying rockfall events—a key manifestation of geological change in high-altitude environments.
Exploring Rockfalls in the Mont-Blanc Massif
Dr. Courtial-Manent’s interest in this research is deeply personal. Living in a region surrounded by mountains, she developed a strong passion for studying the environmental and geological changes that influence the region’s stability and beauty. By investigating how climate change impacts mountain erosion, Dr. Courtial-Manent and her colleagues aim to understand the broader implications of landscape degradation, particularly how it threatens both the natural environment and human activities in the region.
“Our research focuses on understanding how the climate crisis impacts mountain erosion by studying rockfall events in the Mont-Blanc massif. By analyzing the effects of permafrost degradation and freeze-thaw cycles on rock stability, we show that erosion rates are accelerating, which has significant implications for the safety of mountain enthusiasts and professionals, infrastructure and economies,” she explains.
The study centers on the impact of climate change on the stability of rock faces, particularly through the effects of permafrost degradation. In high-altitude areas such as the Mont-Blanc massif, permafrost—soil or rock that remains frozen for extended periods—is a critical factor in maintaining the integrity of rock walls. As global warming causes temperatures to rise, the permafrost in these mountainous regions is beginning to thaw, disrupting the physical structure of the rock and leading to increasing rockfall events.
Methodology: A Comprehensive Approach
To understand the scale and timeline of erosion in the Mont-Blanc massif, the research team used a range of methods to track rockfall events over time. These methods include direct observation, terrestrial laser scanning, and a cutting-edge technique that involves the use of cosmogenic nuclides. Specifically, the team focused on the Mer de Glace basin, an area with large amounts of glacial movement and rockfalls, by employing the beryllium-10 isotope to measure the exposure of rock fragments to cosmic rays. This technique allowed the scientists to gauge the time duration in which specific rock fragments remained stationary before eventually falling.
In addition, the team benefited from a citizen science initiative that began in 2007, which involved local mountaineering guides, hut keepers, and hikers in monitoring and reporting rockfall events. This network of observers provided valuable data, noting specific dates, locations, and estimated rock volumes, along with accompanying photographic evidence and weather conditions that helped create a more robust dataset.
“Mountaineering guides, hut keepers, and mountaineers report if they see a rockfall,” Dr. Courtial-Manent explains. “Then they specify the date and location and provide an estimate of rock volume, trying to be as precise as possible. They can also share pictures of the rockfall and give information about the weather conditions to produce a better overview.”
By combining these various data collection methods—terrestrial laser scanning, direct observations from the citizen science network, and the advanced 10Be isotope data—the research team was able to build a comprehensive picture of erosion rates over the past century and a half. The combination of these methods also helped mitigate the biases and limitations of each approach, allowing for a more accurate and thorough analysis of how the landscape has evolved.
Key Findings: Accelerating Erosion and Increased Frequency of Rockfalls
The team’s findings revealed alarming trends in the erosion rates of the Mont-Blanc massif. For the years between 2006 and 2011, the team observed an erosion rate of more than 4.1mm per year, roughly double the erosion rate estimated during the Little Ice Age. In some isolated rock faces, the erosion rates had increased by as much as five times when compared to previous historical benchmarks.
Less than 6% of the recorded rockfalls involved small blocks under 1m3 in size. In contrast, more than 20% of the events involved rocks between 1m3 and 100m3, and the majority of rockfalls came from large-scale mass movements of rock, often up to tens of thousands of cubic meters in volume. This data highlights a distinct shift in the frequency and scale of rockfall events, indicating that not only are these events occurring more frequently, but their scale is also intensifying.
These larger and more frequent rockfalls can be attributed to the continued degradation of permafrost in the rock walls of Mont-Blanc above 3,800 meters. When water enters cracks in the rock and freezes, it expands, slowly causing the rock to crack and destabilize. As temperatures fluctuate with climate change, these freeze-thaw cycles have become more intense, exacerbating the breakdown of the rock faces. Once the permafrost thaws completely due to warming temperatures, the rock faces lose their structural integrity and become more vulnerable to rockfalls.
“We can say with certainty that this process of permafrost degradation is accelerating,” explains Dr. Courtial-Manent. “We are seeing a profound change in how mountain erosion occurs, with a shift in the magnitude and frequency of rockfalls.”
Implications of Increased Rockfall Activity
The growing frequency of rockfalls in the Mont-Blanc massif has serious consequences for the safety of both mountaineers and local communities. As the rockfalls become more frequent, both hikers and professional mountain guides are faced with the real danger of falling debris, which can cause accidents, injuries, or even fatalities. Infrastructure such as mountain huts, climbing routes, and tourist facilities also faces growing risks, and local economies that depend on tourism may be negatively affected by the increasing instability of the landscape.
Increased rockfall activity also poses potential challenges for scientists and environmental managers who must work to monitor and mitigate these risks. Long-term erosion and rock instability caused by warming temperatures will require improved management strategies and infrastructure adaptation. These challenges will only continue to increase as global warming exacerbates freeze-thaw processes, ultimately leading to further permafrost degradation.
What Lies Ahead: A Harbinger for Other Mountain Regions
The research provides critical insights into the Mont-Blanc massif’s response to climate change, but the implications stretch beyond the French Alps. Similar dynamics of permafrost degradation and accelerated erosion are occurring in other mountain ranges around the world, particularly those in high-latitude regions, like the Himalayas, the Alps, and the Andes.
With continuing climate change, the frequency of rockfalls, landslides, and erosion is expected to rise in these regions as well. In particular, scientists warn that permafrost-dependent landscapes in mountain areas could face long-term destabilization, which would require proactive monitoring and preparedness from affected communities.
Dr. Courtial-Manent notes that “the north faces and rock walls, even at higher altitudes than those studied, are already seeing the impacts of the climate crisis. And based on our current data from the Mont-Blanc massif, I believe that we’ve reached a critical point, perhaps one of no return.”
As for the future, researchers cannot say with certainty how quickly the trends will progress. However, one thing is clear: the acceleration of mountain erosion driven by climate change, particularly through enhanced freeze-thaw processes, will only increase the risks to mountain communities, local economies, and outdoor enthusiasts. The Mont-Blanc massif is not alone, and the findings could serve as an early warning for other vulnerable mountain regions across the globe.
Conclusion
This study in the Mont-Blanc massif represents more than just an academic inquiry into rockfall events and erosion rates. It is a stark reminder of the direct and tangible effects of climate change on landscapes and human safety. The results underscore the urgent need for adaptive strategies to mitigate the growing risks of climate-driven erosion and instability, not only in the French Alps but across other mountain regions worldwide. Through continued research, monitoring, and cooperation with local communities, scientists hope to better understand and potentially mitigate the growing dangers posed by this powerful geological force.
Reference: Léa Courtial-Manent et al, A significant doubling of rockfall rates since the Little Ice Age in the Mont-Blanc massif, inferred from 10Be concentrations and rockfall inventories, Earth and Planetary Science Letters (2024). DOI: 10.1016/j.epsl.2024.119142